The English champions were playing their first European game since firing Premier League-winning coach Claudio Ranieri, and goals from captain Wes Morgan and midfielder Marc Albrighton - and a second half penalty save from Kasper Schmeichel - saw them through. Both the Sevilla defense and Leicester's Wes Morgan flailed at a corner, but Morgan got a knock on the ball sending it into goal.
A minute later, Albrighton was sending the King Power into raptures when he drove a low shot into the corner after Mahrez's cross was poorly cleared by Adil Rami.
Sevilla had ex-Arsenal playmaker Samir Nasri sent-off with 15 minutes remaining for a second bookable offense after a clash with City forward Jamie Vardy.
Juventus join the Premier League champions in the quarter-finals after defeating Porto 1-0, claiming a 3-0 aggregate scoreline in Turin.
However, Leicester have the vital away goal that could be the difference should their offensive form continue.
Little credit was initially afforded to caretaker boss Craig Shakespeare, who had served as Ranieri's assistant throughout his time at the club, for the dramatic and immediate reversal of fortunes.
The Foxes host the La Liga side at the KP Stadium on Wednesday morning, trailing 2-1 on aggregate in the round of 16 tie.
Sara Connor jailed in Bali, Turnbull's Victorian headache
Connor has always maintained her only role was in trying to break up the fight and launching herself between the two brawling men. The judge told the court Taylor had been "legitimately and convincingly proven guilty" of group assault causing death.
"I found it very, very surprising", Sampaoli told his pre-game press conference at the King Power Stadium. While it seemed to get to Sevilla's players, it inspired the home side.
Paulo Dybala scored a penalty on the night to separate the sides.
What a night for Shakespeare, who is only the third Englishman to manage in the knockout stage of the Champions League. Leicester showed plenty of energy and bite, leaving Sevilla whimpering.
"It's not only for the players and manager but one of the biggest games in the club's history".
The Riyad Mahrez of this season has had little on the Mahrez of last, though the Algerian global has certainly excelled in Leicester's fine Champions League run.
On the evidence of the first leg, Leicester's task to overturn the deficit is hugely daunting, but it could easily have been an insurmountable one if the Spanish giants had been even slightly less profligate.
Play continued around them as they touched heads during the fiery confrontation, before Vardy flopped backwards dramatically to exaggerate the contact.
- Hundreds of Radioactive Boars in Fukushima Thwart Residents' Plans to Return Home
- Mass Effect Andromeda Launch Trailer Arrives for Serious Galactic Hype
- Rangers players made me proud after Celtic performance, says Graeme Murty
- German shopping centre shut by police over attack fears
- Nicki Minaj Plays to Her Marketing Strengths Against Remy Ma
- Elon Musk has another ambitious energy project and this time it's free
- Gander Mountain to close stores in Killeen, Waco
- New Michael Brown video raises questions
- Turkey Claims to Have Killed 71 US-Backed Kurds in Syria Attacks
- Post-firing, NY prosecutor's office likely to plot similar course